The manufacture of a thermometer movement featuring a bimetal coil which coils or uncoils in response to changes in temperature is well-known in the art. In the construction of a typical bimetal coil thermometer movement, one end of the bimetal coil--the "stationary end"--is fastened to a stationary support and the other end of the coil--the "unrestrained end"--is directly or indirectly attached to an arrow, needle or other temperature indication device. When a change in temperature causes the bimetal coil to coil or uncoil, the unrestrained end moves. The movement of the unrestrained end of the bimetal coil is then translated to the indication device, thereby changing the position of the indication device relative to a graduated scale. The relative position of the indication device with respect to the graduated scale can then be used to determine the measured temperature.
It is also well-known in the art that the initial position of the indication device with respect to the graduated scale must be calibrated when the thermometer is manufactured or installed. In general, calibration is achieved by rotating the position of the stationary end of the coil, thereby causing the unrestrained end of the coil to move until the indication device points to the temperature on the graduated scale that corresponds to the ambient temperature at the time of manufacture or installation. Past attempts to devise a bimetal coil thermometer movement that can be easily and efficiently calibrated without the use of special tools have not been successful.
For instance, where the stationary end of the bimetal coil is the coil's inner end, past thermometers have mounted the inner end of the coil to a rotatable hub located within the thermometer shell. An opening is located in the rear of the shell so that the hub can be engaged by a suitable tool, such as a screwdriver or Allen wrench. In this manner, the thermometer is calibrated by using the tool to rotate the hub relative to the thermometer shell and thereby coil or uncoil the bimetal coil until the correct temperature reading is obtained.
Past thermometers in which the stationary end of the bimetal coil is its outer end have taken a similar approach. In some such thermometers, the unrestrained end is connected to an arbor rotatably mounted in an aperture in the front part of the thermometer shell. When the unrestrained end of the coil coils or uncoils as a result of a change in temperature, it rotates the arbor, which translates the movement of the unrestrained end to the indication device.
In some of the known thermometers of this type, the bimetal coil is placed in a rotatable drum sandwiched between the front and back parts of the thermometer shell and the outer end of the coil is affixed to the drum. An opening is located in the back part of the thermometer shell so that the drum can be engaged and rotated with a suitable tool, such as a screwdriver or Allen wrench. Rotation of the drum within the thermometer shell causes the bimetal coil to rotate relative to the thermometer shell. This rotation is translated to the indication device by means of the arbor. In this manner, calibration is achieved by using a tool inserted through the back of the thermometer shell to rotate the drum located therewithin until the indication device is aligned with the proper temperature reading.
Prior art thermometers as described above suffer from numerous drawbacks. The most obvious drawback is that the thermometer movement cannot be calibrated without the use of a suitable tool. The necessity of a tool not only makes calibration more difficult and time-consuming, it also makes calibration impossible if the proper tool is not on hand.
In addition, a person attempting to calibrate one of these prior art thermometers must operate a tool inserted through the back of the thermometer movement shell while, at the same time, monitoring the position of the indication device located on the front of the thermometer movement. This is an awkward task that requires a level of dexterity, which makes calibration difficult or impossible for many people.
Moreover, the need to visually observe the thermometer indication device during calibration in order to determine the amount of rotation required creates further difficulties, and can even make calibration impossible when the thermometer is bulky, heavy, affixed to a larger object (such as an incubator or cooler) or mounted to or through a wall to monitor the temperature on the other side of the wall (such as the temperature in a curing or drying room, a refrigerated room or a greenhouse).